Dyspnoea and oxygen therapy in chronic obstructive pulmonary disease

Abstract

Background: Chronic obstructive pulmonary disease (COPD) is common, incurable and characterized by disabling dyspnoea, functional decline and reduced quality of life. The mechanisms underlying dyspnoea in COPD are complex and few strategies have been found to alleviate it. Oxygen therapy has been shown to improve survival for patients with COPD and severe resting hypoxaemia when used for ⩾15 hours per day, long-term.Objectives: This paper reviews factors contributing to dyspnoea in COPD and the role of oxygen therapy in its management.Major findings: The causes of dyspnoea in COPD are not fully understood. Dyspnoea involves an interaction between altered pulmonary mechanics and abnormalities of gas exchange and skeletal muscle. A disparity arises between effort expended to meet ventilatory demand and feedback from chemo- and other receptors, influenced by psychosocial and behavioural factors. Oxygen therapy reduces exertional dyspnoea acutely in COPD with and without hypoxaemia. The use of supplemental oxygen during exercise training may allow higher training intensities to be achieved and thus may be beneficial, but the long-term effects are unknown. There is no evidence that continuous long-term oxygen therapy improves dyspnoea in COPD with severe hypoxaemia. For patients without severe resting hypoxaemia, ambulatory oxygen, provided for use during exertion, confers no benefits upon dyspnoea. Further, there is no evidence to support the use of supplementary oxygen for alleviation of dyspnoea at rest, before or after exertion.Conclusions: In patients with COPD, oxygen reduces exercise-induced dyspnoea acutely, but the relationship between oxygen and dyspnoea in other situations is less clear. A low oxygen level does not always lead to dyspnoea and similarly supplemental oxygen does not always reduce dyspnoea.